Trithionate ion

X-ray diffraction shows the dithionate ion to consist of two triangular pyramids joined at their apices (Fig. 188). In the trithionate ion the third sulphur atom lies between the other two with an S—S—S angle of 103° (Fig. 189). In the tetrathionate and pentathionate ions the additional sulphur atoms are attached to one another in simple chains (Fig. 190). 

Closely related to the trithionate ion are molecules S(S02R)2 and Se(S02R)2 of which the following have been studied in the crystalline state ... 

Fig. 10.07. The structures of some polynuclear sulphur oxy-ions. (<2) The dithionate ion, So062. (b) The trithionate ion, S3062-. (c) The perdisulphate ion, S2082-. (d) The metabisulphite ion, S2052. ...

The S-S distances of 2 15 A in the trithionate ion (and also of 2 01 A in the dithionate ion) are in reasonably satisfactory agreement with the S-S distance of 2 04 A in the S8 molecule of elementary sulphur, in which, also, the sulphur atoms are linked by single covalent bonds. 

A notable feature of the reduction potentials for the four individual reaction steps in Table XXII is that three of the potentials are as low as that of the hydrogen couple, and the fourth is almost as high as in Oz or nitrate respiration. A large part of the total free energy of the sulfate-to-sulfide reaction seems to be concentrated in the trithionate ion so it can be released in one step. It is possible to speculate that the three low potential steps—reduction of sulfate, sulfite, and thiosulfate—are only maintenance level operations, receiving their electrons from a short chain similar to Fig. 41 which produces no ATP. A longer electron transport chain could operate between approximately —450 and -(-381 mV to carry electrons to trithionate, and several ATP could be generated within this potential gap. 

These compounds, disulfonyl mono-, di-, and polysulfides, are intermediates between organic mono-, di-, and polysulfides and the polythio-nates, in the sense that they are formally derived from the polythionic acids by substitution of alkyl or aryl groups for the hydroxyl groups of the acids. The monosulfides, like the trithionate ion, contain three sulfur atoms in a chain, but only the middle one is divalent. There is thus no real structural problem with regard to branching or nonbranching in disulfonyl monosulfides and trithionates. 

Potassium trithionate is orthorhombic bipyramidal, space group D -Pnma with four formula units per unit cell. From Zachariasen s (239) structure analysis, carried out in the early thirties by trial and error methods, the trithionate ion has mirror plane symmetry in the crystals, lying with all three sulfur atoms and two of the oxygen atoms in the mirror plane. The rubidium salt (161) is isomorphous with the potassium salt. The third trithionate for which data are available, the thallium salt, is monoclinic prismatic, space group Ca ,6-C2/c with four formula units per unit cell (151). Here, the trithionate ion has a twofold axis as symmetry element. 

The displacement on the trithionate ion 8(803) takes place at the central divalent sulfur (94) via a transition state resembling that of the 8n2(C) reaction. The increasing effectiveness of the bases CN < PhjP < PhS < EtS has been established. 

Until a few years ago, however, the cations 1 and 2 had aroused little interest. In 1947 Liittringhaus and Bottcher2 recognized the products of the reaction of l,2-dithiole-3-thiones ( trithiones ) with alkyl esters of inorganic acids as 3-alkylmercapto derivatives of the 1,2-dithiolium system these authors explained certain apparently unusual physical and chemical properties of these salts by resonance stabilization of the 1,2-dithiolium system.8 Thus these trithionium salts were the first derivatives of the 1,2-dithiolium ion to be identified with certainty. 

The 3-mercapto-1,2-dithiolium salts (39a) also suffer deprotonation on addition of water. This behavior is the basis of a simple and effective method of purification, which is particularly useful for aryl-substituted trithiones. 48 The tendency towards charge neutralization in the alkylmercapto-1,2-dithiolium ions is also the reason for the relative ease of removal of the alkyl group (cf. thermal dealkylation, transmethylation), as well as for the extremely labile bonding of other groups such as acyl—, —S02—, —SO—, —S2C1, and halogen to the exocyclic S atom of the corresponding 3-mercapto-1,2-dithiolium derivatives. 

These anions, S 06, with n up to 22 or higher, can be separated chromatographically only lower members are well characterized. They are normally named according to the total number of sulfur atoms, namely, trithionate, S3C, and so on. They are occasionally called sulfane-disulfonates, for example, disulfanedisulfonate for S4062-. The free acids are unstable as are also the HS 06 ions. 

The pK value has so far been determined only for the protonation of 2H-thiopyran-2-thione.88 The protonation takes place ontheexo-cyclic atom, giving a structure resembling a derivative of the pyrylium (X = 0) or thiopyrylium (X = S) ion. Comparative measurements have also been carried out for trithione (Table XIV). It is evident that... 

The kinked structures of the trithionate and perdisulphate ions is clear evidence that the bonds within these groups are not ionic, and in fact both ions can be satisfactorily formulated in terms of a picture in which the binding throughout is by single covalent bonds ... 

The stoicheiometry and kinetics of reaction of aqueous ammonia solutions of copper(ii) ions with thiosulphate ion in the presence of oxygen have been examined. The amount of oxygen consumed and the relative amounts of the final sulphur products, namely trithionate and sulphate ions, are dependent on the initial 8203 concentration and pH. The most active species for SjOe" formation is a tetra-amminecopper(ii) complex having one axial 8303 and one axial O2 ligand. A complex having both axial and equatorial 8203 ligands as well as an axial O2 was suggested as the reactive intermediate for sulphate formation. 

SO far, is incapable of existing even in dilute solution, the 1,2-dithiol-ium ion (1) is surprisingly stable. It is similar in this respect to the thermally very stable trithiones or to the structurally related thiurets, with which it probably shares the property of having a practically planar structure (Section II, C, 2). 

Sulfur Melting. Under the temperature conditions used in the sulfur melting step (>125°C) there is some thiosulfate decomposition. The reaction consumes hydrogen ions and forms sulfur and sulfate as products. The ratio found of 1.37 moles of sulfur formed per mole of thiosulfate reacted suggests that the main form of the decomposition involves formation of sulfur and bisulfite from the thiosulfate, followed by decomposition of the bisulfite (5) via trithionate to sulfate. The sequence is ... 

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